In a multi-cylinder engine, such as a V-6 marine engine, a cylinder head is associated with each bank of cylinders, and in the past the conventional head has been composed of two cast metal sections, including a head section that enclosed the cylinders and an outer cover section that defines with the outer surface of the head section a water cooling passage. In the assembled engine, water from the block is introduced into one end of the cooling passage in the head and discharged from the opposite end of the passage.
In the conventional cylinder head construction, the two sections are individually cast and the mating faces are then machined, holes are drilled and tapped and the cover section is subsequently connected to the head section through a gasket and bolts. The section thickness of the mating surfaces must be increased to provide the necessary gasket width for effective sealing. In addition, holes are drilled in the flange of the head section to receive bolts when assembling the head to the engine block. This procedure is extremely labor sensitive which adds substantially to the overall cost of the engine, and the need for gaskets, bolts and the increased section thickness at the mating surfaces results in a considerable increase in material cost. Moreover, the gasketed joint provides a potential leakage site.
Evaporable foam casting procedures have been used to produce engine blocks and other engine components, particularly those having complex contours. In the evaporable foam casting procedure, a pattern is formed of an evaporable foam material, such as polystyrene, and is identical in configuration to the metal part to be cast. The pattern is placed in a mold and a flowable material, such as sand, is introduced into the mold and surrounds the pattern as well as filling the cavities in the pattern. In the casting process, molten metal is introduced into the mold through a sprue and the heat of the molten metal will vaporize the foam material with the vapor being trapped within the intersticies of the sand, while the molten metal will fill the voids created by vaporization of the pattern to provide a cast metal part which is identical in configuration to the evaporable foam pattern.